HP11C ++

[Mike T.]

Did anyone ever get to the bottom of this ...?

https://www.hpmuseum.org/cgi-sys/cgiwrap...read=11083

[damaltor]

This is very interesting. I might have a few parts left, but they are in storage and i am pretty sure that i dont have a fitting calculator to try...

[Dave Britten]

Quite intriguing. I'd be reluctant to open up any of my 11Cs and 15Cs and start moving chips around to see what happens, but this might be something that could be experimented with using an emulator to find out if the 11C ROM does indeed support additional memory. The 42S can be upgraded from 8 KB to 32 KB by simply swapping the SRAM chip and closing a jumper on the PCB to tell the "OS" to use more RAM, so maybe something similar is possible in the 11C!

It's also worth mentioning that Swiss Micros has a special firmware for their DM15L that provides additional memory (can't remember how much, but it's enough that I'm tempted to order one). Figuring out how they patched the ROM and/or emulator for that model might be a good place to start.

[J-F Garnier]

No need to move chips.
Since this 20-years old post, we got "true emulators" (meaning: that use the genuine ROM), starting from Nonpareil (well, it didn't use the "genuine" ROM but that's not important here).
And the result is: nothing happens if you plug more RAM registers.

To make the 15C ROM use the extra registers, several ROM locations must be changed (patched). SwissMicros and a few others did it.
I'm not aware that it has been done or is even possible with the 11C.

My hypothesis about the special 11C mentioned in the original post: it may be a HP-15C board mounted inside a HP-11C housing.
Since the 11C and 15C keyboards are very similar, it may give the impression, with just a quick inspection, of a 11C with 448 program steps.
Of course I may be wrong.

J-F

[Dave Britten]

Occam's razor suggests that's probably the best theory. You'd have to go digging into the shifted functions to really tell the two apart.

[brouhaha]

(01-30-2022 02:04 PM)Mike T. Wrote:  Did anyone ever get to the bottom of this ...?

https://www.hpmuseum.org/cgi-sys/cgiwrap...read=11083

By now I imagine that you, and everyone who is interested, knows the answer, but for the record...

The extra chip in the 15C is the second R2D2, with the display signals not bonded out. Some, but not all, Voyager calculators of other models had the footprint for the second R2D2, in order that a common PCB could be used for all models.

None of the Voyagers have microcode to dynamically recognize more memory.. Puting the 15C second R2D2 into any other model will not (by itself) accomplish anything.

The first R2D2 in any Voyager holds ROM addresses 0x0000..0x17ff, RAM addresses 0x00..0x07, and the display registers at 0x09..0x0a.

The second R2D2 in the 15C holds ROM addresses 0x2000..0x37ff, RAM addresses 0x10..0x17, and (unused) display registers 0x19...0x1a. The 15C uses the second R2D2 display registers as scratch space, although the low six bits of those registers are believed to be unimplmented.